Expandable intervertebral spacers and methods of use

ABSTRACT

An intervertebral spacer is inserted between vertebral members in a compact configuration and expanded post-insertion to contact the adjacent vertebral members. The intervertebral spacer comprises a first member and a second member movable with respect to the first member between retracted and extended positions.

RELATED APPLICATION

The present application is a continuation application of U.S. patentapplication Ser. No. 11/415,042 filed on May 1, 2006 and hereinincorporated by reference in its entirety.

BACKGROUND

The present application is directed to devices and methods forstabilizing vertebral members, and more particularly, to intervertebralimplants and methods of use for replacing an intervertebral disc,vertebral member, or combination of both to distract and/or stabilizethe spine.

The spine is divided into four regions comprising the cervical,thoracic, lumbar, and sacrococcygeal regions. The cervical regionincludes the top seven vertebral members identified as C1-C7. Thethoracic region includes the next twelve vertebral members identified asT1-T12. The lumbar region includes five vertebral members L1-L5. Thesacrococcygeal region includes nine fused vertebral members that formthe sacrum and the coccyx. The vertebral members of the spine arealigned in a curved configuration that includes a cervical curve,thoracic curve, and lumbosacral curve. Intervertebral discs arepositioned between the vertebral members and permit flexion, extension,lateral bending, and rotation.

Various conditions may lead to damage of the intervertebral discs and/orthe vertebral members. The damage may result from a variety of causesincluding a specific event such as trauma, a degenerative condition, atumor, or infection. Damage to the intervertebral discs and vertebralmembers can lead to pain, neurological deficit, and/or loss of motion.

Various procedures include replacing the entirety or a section of avertebral member, the entirety or a section of an intervertebral disc,or both. One or more replacement implants may be inserted to replace thedamaged vertebral members and/or discs. The implants reduce or eliminatethe pain and neurological deficit, and increase the range of motion.

SUMMARY

The present application is directed to an intervertebral spacer withfirst and second members each with an outer side and an inner side. Themembers may be positioned in a stacked orientation with the inner sidesfacing together. A threaded extension may extend outward from the innerside of the first member. A cavity may be formed on the inner side ofthe second member, and may include a floor opposite from an open side. Aring gear may be positioned in the cavity and against the floor. Thering gear may include a threaded bore that receives the threadedextension and teeth that extend around an outer circumference. A gearmay be positioned in the cavity and may include helical teeth thatengage with the teeth on the ring gear. The gear may be rotatablypositioned in the cavity with rotation in a first direction causing thefirst and second members to move apart and rotation in a seconddirection causing the first and second members to move together.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an exemplary intervertebral spacer in aretracted position.

FIG. 2 is a perspective view of an exemplary intervertebral spacer in anextended position.

FIG. 3 is an exploded perspective view of an exemplary intervertebralspacer.

FIG. 4 is an exploded perspective view of an exemplary intervertebralspacer.

FIG. 5 is a perspective view of an exemplary intervertebral spacer in aretracted position.

FIG. 6 is a perspective view of an exemplary intervertebral spacer in anexpanded position.

FIGS. 7 and 8 illustrate an exemplary method of inserting theintervertebral spacer.

DETAILED DESCRIPTION

The present application relates to implants for replacing anintervertebral disc, vertebral member, or combination of both, and tomethods of inserting the same. The implant comprises an intervertebralspacer 10 that can be inserted between vertebral bodies in a compactconfiguration as shown in FIG. 1 and subsequently expanded to contactthe adjacent vertebral bodies as shown in FIG. 2.

FIGS. 3-6 illustrates one exemplary embodiment of the intervertebralspacer 10. The intervertebral spacer 10 comprises an inferior member 12and a superior member 60 movable with respect to the inferior member 12from a retracted position to an extended position. A jack mechanism 60is interposed between the inferior member 12 and superior member 40 formoving the superior member 60 between the retracted and extendedpositions.

The inferior member 12 comprises a body 14 including a bottom surface 16that contacts an adjacent vertebral body. The bottom surface 16 can betextured to grip the adjacent vertebral body. For example, small teeth,ridges, or grooves can be formed in the bottom surface 16 to improvegripping capability. The body 14 has a main cavity 18 formed therein tohouse components of the jack mechanism, and a guide hole 20 to receive aguide member 46 on the superior member. The body 14 further includes ashelf 22 having an opening 24 formed therein. The shelf 22 and opening24 are configured to engage the head of an insertion tool 100 as will behereinafter described in more detail.

The superior member 40, shown in FIGS. 5 and 7, comprises a plate 42having a top surface 44 that engages an adjacent vertebral body. The topsurface 44 can be textured to grip the vertebral body. For example,small teeth, ridges, or grooves can be formed in the top surface 44 toimprove gripping capability. The top plate 42 is shaped to generallycorrespond to the shape of the inferior member 12. Guide member 46extends downward from the top plate and fits within the guide hole inthe inferior member 12. The top plate 42 further includes a tab 50 withan opening 52 formed therein to engage the insertion tool 100.

The jack mechanism 60 comprises a screw shaft 62 that extends downwardfrom the bottom surface of the top plate 42, and a ring gear 64 that isrotatably mounted in the main cavity 18 of the inferior member 12. Thering gear 64 is internally threaded to mesh with the externally threadedscrew shaft 62. When the ring gear 64 is rotated in a first direction,the superior member 40 is raised relative to the inferior member 12.Conversely, when the ring gear 64 is rotated in a second direction, thesuperior member 40 is moved toward the inferior member 12.

A drive gear 70 meshes with the ring gear 64. The drive gear is actuatedby the surgeon to rotate the ring gear 64. In the exemplary embodiment,the drive gear comprises a worm gear with helical teeth that mesh withthe teeth of the ring gear 64. The drive gear 70 has an axial bore 72 toreceive a mounting shaft 74 which is rotatably journaled in openings 76,78 in the main cavity 14 of the inferior member 12. The mounting shaft74 includes a head 75 having a socket for receiving a tool. The drivegear 70 may be fixed to the mounting shaft 74 by any suitable means,such as pin 80. During assembly, the ring gear 64 and drive gear 70 aredisposed within the main cavity 14 of the inferior member 12 as shown inFIG. 4. The axial bore 72 of the drive gear 70 is aligned with openings76, 78 in the main cavity 14 of the inferior member 12. The mountingshaft 74 is inserted through the aligned openings in the wall of themain cavity 14 and through the axial bore of the drive gear 70. Afterthe mounting shaft 74 is inserted, the drive gear 70 is secured to themounting shaft 74, for example, by pin 80.

The inferior member 12 and superior member 40 can be made of anysuitable material, such carbon reinforced PEEK. The bottom of theinferior member 12 and/or top plate 42 of the superior member 40 couldbe porous to allow the in-growth of bone. An embedded biologic coating,such as hydroxia appetite (HA), BMP, or calcium phosphate could be usedto promote bone in-growth. The contact surfaces of the inferior andsuperior members 12 and 40 could also be textured to grip the adjacentvertebral bodies.

In use, the superior member 40 is assembled to the inferior member 12and placed in a compact configuration with the superior member 40 in aretracted position relative to the inferior member 12 as shown in FIG.5. The intervertebral spacer 10, in a compact configuration, is insertedthrough a cannula 150 into an intervertebral space between two vertebralbodies. Those skilled in the art will appreciate that the intervertebralspacer 10 can be used to replace one or more discs and/or vertebralbodies. After the insertion of the intervertebral spacer 10, the drivegear 64 is rotated to cause the superior member 40 to extend away fromthe inferior member 12 as shown in FIG. 6. The superior member 40 israised until the contact surfaces 16, 44 of the inferior and superiormembers 12 and 40 are engaged with the adjacent vertebral bodies. Thegear teeth on the ring gear 64 and drive gear 70 are formed so as tolock at any selected height.

The intervertebral spacer 10 may be used in various regions of thespine, including the cervical, thoracic, lumbar and/or sacral portionsof the spine. FIGS. 7 and 8 illustrate an exemplary insertion tool 100that can be used to insert the intervertebral spacer 10. FIGS. 10 and 11illustrate accessing the spine from a postero-lateral approach. Thoseskilled in the art will appreciate that other approaches may also beused, including posterior, anterior, antero-lateral and lateralapproaches to the spine.

FIGS. 7 and 8 illustrate an exemplary insertion tool 100 to insert theintervertebral spacer 10. The insertion tool 100 includes an elongatehousing 102 having three lumens 104, 106, and 108 formed therein, anengaging tool 110, and a push rod 120. Access to the intervertebralspace is gained through a cannula 150 inserted into the body. FIGS. 7and 8 illustrate the distal end of the cannula 150 and insertion tool100. The engaging tool 110 includes an elongate shaft 112 that passesthrough the center lumen 106 in housing 102, and a cylindrical head 114to engage the intervertebral spacer 10. As shown in FIG. 5, thecylindrical head 114 of the engaging tool 110 is configured to engage inopenings 22, 52 on the inferior member 12 and superior member 40respectively when the superior member 40 is moved to the retractedposition. The intervertebral spacer 10 can rotate freely about the axisof the cylindrical head 104 during insertion to accurately position theintervertebral spacer 10. As the intervertebral spacer 10 is advancedthrough the cannula 150, the intervertebral spacer 10 initially assumesthe position shown in FIG. 7. When the intervertebral spacer 10 exitsfrom the end of the cannula 150, a push rod 104 inserted through lumen104 in housing 102 is used to rotate the intervertebral spacer 10 intothe proper angular position as shown in FIG. 8. A tool (not shown) canthen be inserted through the lumen 108 to engage and rotate the mountingshaft 74. Rotation of the mounting shaft 74 causes the drive gear 64 torotate, which in turn rotates the ring gear 64. Rotation of the ringgear 64 causes the screw shaft 62 to move axially upward raising thesuperior member 40 into contact with the superior vertebral body.

The embodiments described above include member 40 being a superiormember and member 12 being inferior. In another embodiment, theorientation of these members 40, 12 may be interchanged with member 40functioning as an inferior member and member 12 functioning as asuperior member.

The term “distal” is generally defined as in the direction of thepatient, or away from a user of a device. Conversely, “proximal”generally means away from the patient, or toward the user. Spatiallyrelative terms such as “under”, “below”, “lower”, “over”, “upper”, andthe like, are used for ease of description to explain the positioning ofone element relative to a second element. These terms are intended toencompass different orientations of the device in addition to differentorientations than those depicted in the figures. Further, terms such as“first”, “second”, and the like, are also used to describe variouselements, regions, sections, etc and are also not intended to belimiting. Like terms refer to like elements throughout the description.

As used herein, the terms “having”, “containing”, “including”,“comprising” and the like are open ended terms that indicate thepresence of stated elements or features, but do not preclude additionalelements or features. The articles “a”, “an” and “the” are intended toinclude the plural as well as the singular, unless the context clearlyindicates otherwise.

The present invention may be carried out in other specific ways thanthose herein set forth without departing from the scope and essentialcharacteristics of the invention. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive, and all changes coming within the meaning and equivalencyrange of the appended claims are intended to be embraced therein.

1-20. (canceled)
 21. An intervertebral spacer comprising: an inferiormember including a body having a bottom surface being configured tocontact a vertebral body, the body defines a main cavity therein; asuperior member including a plate having a top surface being configuredto engage an adjacent vertebral body, the top surface including a guidemember extending therefrom; a guide hole disposed in the main cavitybeing configured to receive the guide member; and a jack mechanismdisposed in the main cavity, wherein the jack mechanism is configured tocause the inferior and superior members to move in a first directionsuch that the inferior and superior members move apart and in a seconddirection such that the inferior and superior members move towards eachother.
 22. The spacer of claim 21, wherein the top surface includes ashape substantially similar to a shape of the inferior member.
 23. Thespacer of claim 21, wherein the body further comprises a shelf having anopening configured to engage a head of an insertion tool.
 24. The spacerof claim 21, wherein the top surface further includes a tab having anopening formed therein to engage an insertion tool.
 25. The spacer ofclaim 21, wherein the jack mechanism includes a screw shaft extendingfrom a bottom surface of the plate and a ring gear rotatably mounted inthe main cavity, wherein the ring gear is internally threaded to meshwith the externally threaded screw shaft such that when the ring gear isrotated in a first direction, the superior member is raised relative tothe inferior member and when the ring gear is rotated in a seconddirection, the superior member is moved toward the inferior member. 26.The spacer of claim 25, wherein a drive gear meshes with the ring gear64, the drive gear being configured to rotate the ring gear.
 27. Thespacer of claim 26, wherein the drive gear includes a worm gear withhelical teeth that are configured to mesh with teeth of the ring gear.28. The spacer of claim 25, wherein the drive gear includes an axialbore configured to receive a mounting shaft being rotatably journaled inthe main cavity of the inferior member, the mounting shaft includes ahead having a socket for receiving a tool.
 29. An intervertebral spacercomprising: first and second members each with an outer side and aninner side, the first and second members positioned with the inner sidesfacing each other; a cavity extending into the inner side of the secondmember; a threaded extension that extends outward from the inner side ofthe first member and extends into the cavity; a ring gear positioned inthe cavity and including an interior threaded bore that receives thethreaded extension, the ring gear further including an exterior surfacewith a plurality of radial teeth that extend away from the bore and arelongitudinally spaced between non-toothed sections; a rotational memberpositioned in the cavity and including helical teeth that engage withthe plurality of teeth on the ring gear; and the spacer positionablebetween retracted and extended orientations with the first and secondmembers spaced a greater distance apart in the extended orientation. 30.The spacer of claim 29, wherein the threaded extension includes aterminal end spaced away from the first member, with the threadedextension sized for the terminal end to remain within the ring member inthe retracted and extended orientations.
 31. The spacer of claim 29,wherein the cavity includes a floor opposite from an open side and thering gear remains in contact with the floor in the retracted andextended orientations.
 32. The spacer of claim 29, wherein alongitudinal axis of the ring gear is offset from a longitudinal axis ofthe threaded extension such that the axes do not intersect.
 33. Thespacer of claim 29, wherein the plurality of radial teeth extend arounda circumference of the ring gear.
 34. The spacer of claim 29, whereinthe rotational member is a worm gear with a central opening and thehelical teeth extending along an exterior surface.
 35. The spacer ofclaim 29, wherein a height of the second member measured between theinner and outer sides is less than a length of the outer side measuredperpendicular to the height.
 36. An intervertebral spacer comprising: afirst member with a plate having an outer contact surface and an innersurface with an outwardly-extending threaded extension that includes aterminal end; a second member with an outer contact surface and an innersurface, the inner surface of the second member facing towards the innersurface of the first member and including a cavity that aligns with theextension, the cavity including a floor; a ring gear positioned in thecavity and including a threaded bore that receives the threadedextension, the ring gear further including an exterior surface withradial teeth; a rotational member positioned in the cavity and includinghelical teeth that engage with the teeth on the ring gear; and thespacer positionable between retracted and extended orientations with thefirst and second members spaced a greater distance apart in the extendedorientation; the terminal end of the first member remaining with thering gear in the retracted and extended orientations.
 37. The spacer ofclaim 36, wherein the radial teeth of the ring gear extend around acircumference of the ring gear and are positioned along a longitudinalaxis of the ring gear between non-toothed sections at first and secondends of the ring gear.
 38. The spacer of claim 36, wherein a height ofthe second member measured between the inner and outer sides is lessthan a length of the outer contact surface.
 39. The spacer of claim 36,wherein the ring gear is positioned against the floor of the cavity inthe retracted and extended orientations.
 40. The spacer of claim 36,wherein the first member includes a second extension that extendsoutward from the inner surface and is spaced away from the threadedextension, the second extension sized to fit within a second cavity inthe second member when the spacer is in the retracted orientation.